There is no convenient time for everyone.
As of now, no guild can hold Sacred for more than one WoE, and Prontera barely gets broken. Payon gets plenty of action, especially for a population of ~350 every WoE. There are 5-10 guilds after it at once. But no one can break Prontera defense well enough to keep the castle. So the majority of rucksacks are coming from Prontera and going into one guild.
What's to stop this from happening if we have a Eurasian WoE, especially if there is only one castle open at one time. Then players will complain about that. This is, after all, a concern about WoE drop only being obtained by Americans or whoever WoE during the current WoE time, right? What's going to stop a large Eurasian guild from taking and keeping the Eurasian castle.
There is a reason why rucksacks are not in great circulation, and that the ones that are available aren't being sold. Trans managed to bring up their economy and keep their castle, so the deviling bags are staying with them for the most part. And since half a dozen guilds fight over Payon, angeling bags are a rarity. The WoE time has just as much to do with the circulation of WoE drops as the way the players fight over the castles. If Trans hadn't secured Prontera like it has, rucksacks would be very rare, and we wouldn't have this issue.
To be blunt, Trans has a monopoly of Deviling bags, but that's good for them. They managed to keep their castle, and now no one can break past them, because all the guilds are busy squabling over Payon, instead of working together to go after Prontera.